Nyala Antelope Vomiting During Capture and Chemical Immobilization
The nyala (Tragelaphus angasii) is a member of the spiral-horned antelope genus that includes the kudu and eland. More slightly-built than these antelopes, the nyala is noted for its extreme sexual dimorphism and specialized habitat and feeding preferences that limit its distribution.1 The bulls have long, inwardly-curved horns and a white chevron on their faces and a charcoal-grey, shaggy coat. They stand approximately 106 cm (42 inches) tall and weigh in at around 98–125 kg.
The females are much smaller and do not have horns. Females and young have short, brighter chestnut-colored coats with 8–12 white stripes on the torso, with spots and bands on the legs, chest, and cheeks, and a bushy tail.
The nyala is a cover-dependent browser and grazer that occupies dense woodlands on the coastal plains and major river valleys of eastern Africa from southern Malawi to Natal.2 Their habitats include lush grasslands next to the cover where these animals spend the day; at night, they emerge to graze during the rainy season. Females and young live in small herds of five or six animals. The males are nonterritorial and occupy overlapping ranges.
Chemical Immobilization and Vomiting in Nyala
The chemical immobilization of nyala is sometimes necessary in the field as well is in the preserve or zoo setting. Vomiting is one of the more common post-sedation and post-anesthesia complications that can arise in these animals. In humans and animals, vomiting once or twice after a surgical procedure is often considered normal however, if the vomiting continues, it can be a sign of an emerging complication. A far more serious complication involves vomiting that occurs during a procedure, as this can pose grave risks due to anesthetic aspiration.
Anesthetic aspiration involves an animal vomiting food from their stomach during a surgical procedure, which subsequently infiltrates into the lungs. This can lead to aspiration pneumonia. While modern protocols for anesthesia and sedation in wildlife are generally safe, respiratory complications such as anesthesia-related aspiration and pneumonia can be fatal after the fact.
Acute intraoperative aspiration (aspiration during a surgical procedure) is a potentially fatal complication with significant associated morbidity. Animals undergoing thoracic surgery are at increased risk for anesthesia-related aspiration, largely due to the predisposing conditions associated with this complication. Awareness of the risk factors, predisposing conditions, precautions to decrease risk and immediate management options by the veterinarian is imperative to reducing risk and optimizing outcomes associated with this complication.3
Unfortunately, in the case of chemically immobilized wildlife, it is often impossible to perform the sorts of presurgical assessments that are routine and even required for human patients. Therefore, attending wildlife and research veterinarians must be prepared for the possibility of anesthetic aspiration in nyala.
Reducing Risk Factors
The veterinary care of non-domestic hoofstock such as nyala has become commonplace due to the integration of veterinary medicine in wildlife management programs, zoological collections, exotic animal ranching expansions and the private collection of wildlife species.4 The sedation and anesthesia of nyala requires the knowledge the pharmacology of the drugs being used, as well as the wide variation in dose response among sub-species of these animals. A major challenge for the wildlife veterinarian or manager is correlating the available pharmaceutical tools with the environment and conditions, as well as the procedures and events preceding, during, and following the anesthetic event.5 For example, an anesthesia protocol that’s practical in a fenced captive environment may not be appropriate in the field.
Today, the quality of sedation, anesthesia and analgesia achievable in antelopes and other wildlife species has been made possible through the availability of new, receptor-specific and highly potent agonist-reversible pharmaceuticals and the improved knowledge of CNS receptors.
Antelope Biology
Antelope are a diverse collection of ruminants, “antelope” being the name given to members of the families Antilocapridae and Bovidae. The pronghorn antelope, Antilocapra americana, is the only member in the Antilocapridaefamily.5 Antelope males and the females of some species have unbranched horns attached to the frontal bones of the skull.4 Until the advent of potent opiates, the pronghorn was very difficult to safely capture or anesthetize.5 Although carfentanil was reported as effective in many captures, more recently, the combination of butorphanol and azaperone have become popular in the chemical immobilization of pronghorn.
According to the available literature, each species of antelope has its own anesthesia recommendation with intra-species variations of dosages because of diverse individual responses to anesthetic agents.4,5 These variations represent risks for vomiting and anesthetic aspiration in these species, and attendant factors (e.g., stress, venue, individual animal and field conditions) must also be taken into account.
Preventing and Managing Anesthetic Aspiration in Nyala
Monitoring core body temperature is essential when sedating or anesthetizing nyala.5 Hyperthermia and subsequent capture myopathy are commonly-encountered problems with antelopes. Intubation is widely recommended for an anesthetized nyala that needs to be transported or anesthetized for greater than one hour. Until the more recent use of formulated drugs (e.g., combinations of α2-agonists such as medetomidine, detomidine, xylazine and their reversal agents), opioids—which are often associated with vomiting in many species—were the mainstay of antelope anesthesia in wildlife and captive care.5
For the prevention of anesthetic aspiration in nyala, histamine (H2) antagonists such as cimetidine, famotidine, nizatidine, and ranitidine and proton pump inhibitors (PPIs) such as dexlansoprazole, esomeprazole, lansoprazole, omeprazole, pantoprazole, and rabeprazole have been shown to be effective in increasing the pH and reduce the volume of gastric contents.3 Additionally, prokinetics (e.g., domperidone, metoclopramide, erythromycin and renzapride) promote gastric emptying and are believed to reduce the risk of aspiration.3
If gastric content is seen in the oropharynx or the airways, the animal should be immediately positioned with its head down and rotated laterally if possible.3 Orotracheal and endotracheal suctioning is indicated (either before or after orotracheal intubation), depending on whether regurgitation continues and if the airway is visible. The airway should be secured as rapidly as possible to prevent further contamination and to facilitate airway clearance.6 Flexible bronchoscopy is an important adjunct to orotracheal and endotracheal suctioning, and having a flexible bronchoscope available is a sound prophylactic measure. If particulate matter is present in the airway, rigid bronchoscopy is indicated.3,6
3Nason, K. Acute Intraoperative Pulmonary Aspiration. Thoracic surgery clinics vol. 25,3 (2015): 301-7.
4Lance, W. Exotic Hoof Stock Anesthesia and Analgesia: Best Practices. In: Proceedings, NAVC Conference 2008, pp. 1914-15.
5Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014, https://doi.org/10.1002/9781118792919.ch60.
6Kluger M.T., et. al. Crisis management during anaesthesia: regurgitation, vomiting, and aspiration. Quality & safety in health care. 2005;14(3): e4.
About NexGen Pharmaceuticals
NexGen Pharmaceuticals is an industry-leading veterinary compounding pharmacy, offering sterile and non-sterile compounding services nationwide. Unlike other veterinary compounding pharmacies, NexGen focuses on drugs that are difficult to find or are no longer available due to manufacturer discontinuance or have yet to be offered commercially for veterinary applications, but which still serve a critical need for our customers. We also specialize in wildlife pharmaceuticals, including sedatives and their antagonists, offering many unique options to serve a wide array of zoo animal and wildlife immobilization and anesthesia requirements.
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